As it is a well known fact, the water discharge of the water delivering drilled wells depends in addition to the layer conditions on the mode of the well formation, the age of the well, the methods of water production and on the quality of water.
The mode of well formation includes the structural solutions to be applied. e.g. the piping, the arrangement and construction of the filter, as well as the drilling methods and pumping with the purpose of cleaning being utmost important from the point of view of water discharge. The pumping serving for purification may decisively influence the quality of well formation, which can be characterized numerically by the well-resistance. As it is known, the components of well-resistance are the following: the dam effect, i.e. the changed resistance of the zone around the well, the layer resistance, the filter resistance, the resistance resulting from the enstrustation, the resistance-surplus of a more or less turbulent stream--compared to the linear stream--at higher flow velocities and at least the flow resistance of the piping in the well.
By the application of the process according to the invention the increase of the water discharge can be achieved by a considerable decrease of the dam effect--the more, by converting it into an effect with a different sign (achieving a lower resistance in the zone around the well, than the original one), by the reduction of the resistance resulting from encrustation and indirectly by the reduction of the resistance-surplus of the turbulent stream.
It is a fact of common knowledge, that the resistance of the zone around the filter can be reduced by pumping, for this purpose the so-called Mammoth pump or a compressor is used. The pumping method in itself rarely yields satisfactory results. In the majority of cases the reason for the insufficient effect of pumping is, that the pressure drop in the well does not entirely break up the conglomerated layer in the clogged zone around the filter, but only in certain places. The water streaming along the lowest resistance in the initially small channels having been formed in such a manner--forms more and more larger ducts resulting finally in the collapse of the layer. In this case the whole cleaning process has to be repeated.
Encrustation, i.e. clogging is caused by the deposition of different compounds; said compounds contain mainly iron and calcium in the form of carbonates, oxides, hydroxides, sulfates and silicates. Due to biological effects, e.g. as a consequence of the activity of iron- and manganese bacteria organic compounds may also deposit. The rate of encrustation increases in proportion to the age of the well, at the same time the mode of operation and the quality of water are also considerably influence the rate of incrustation. The so-called "ochre-formation" is the largest problem, accordingly, it is to be considered as the most dangerous phenomenon; the course of this process iron compounds, mainly ferric(lll)hydroxide are segregated. According to our experiences, the intensity of draw-off plays an inportant role in ochre-formation. The partial or total turbulence arising with higher flow velocities considerably increases the rate of ochre-formation, while with wells which are out of operation ochre-formation usually could not be observed.
In order to be able to eliminate the layer purification by means of pumping, mostly a treatment with hydrochloric acid has been used (E. Bieske: Handbuch des Brunnenbaus, Berlin, 1965). Hydrochloric acid dissolves the oxides and carbonates and elution of the ferrous and calciferous deposits in the form of chlorides from the filter zone becomes possible. However, treatment with hydrochloric acid may be disadvantageous in several cases, e.g. where the relatively rapid and strong dissolving effect may result in the collapse of layers, in addition to this, due to its metal dissolving effect, hydrochloric acid is highly damaging to all of the fittings made of steel. In spite of the known damaging effects, improvement of wells with a reduced water discharge is mostly performed by using hydrochloric acid (Technical Directives of the Office of Water Conservancy, 136/4-73/4.2). The layer purification with hydrochloric acid causes corrosional damage in the metal parts and in the case of glassfibre-reinforced synthetic casing pipes the risk is extraordinarily high and may lead to the early aging of the well.